Heterogeneity of nanoporous solids in adsorption from solutions—evaluation of energy distribution functions for adsorption in micropores of activated carbons by a comparative method

Abstract

Abstract The concept of a comparative method to analyse the porous structure of activated carbons by means of solid–liquid excess-adsorption isotherms is presented. This method is based on a comparison of the excess-adsorption isotherm for benzene (1) cyclohexane (2) mixtures on a nanoporous active carbon with that measured on a non-porous reference adsorbent. The proposed approach gives the possibility for estimating the maximum amounts adsorbed in the micropores and on the surface of mesopores within the nanoporous material. Consequently, the total surface phase capacity can be determined. The partial excesses for micro- and mesopores may be extracted from the total adsorption excess. As the comparative method is based on a linear equation (the so-called “ n / x ”-plot), a suitable statistical analysis of errors can been applied. The energy-distribution function is used to characterize heterogeneity effects. A regularization method has been employed, which takes into account the ill-posed character of the integral equation. The partial excess-adsorption isotherm, evaluated for micropores may be analyzed with regard to structural heterogeneity properties of nanoporous solids. Two series of modified active carbons, i.e. active carbons prepared from plum stones and synthetic active carbons, were used in these studies.